Stability of ultra-high-temperature ZrB2–SiC ceramics under simulated atmospheric re-entry conditions

Microstructure modifications of an ultra-high temperature ZrB2–SiC ceramic exposed to ground simulated atmospheric re-entry conditions were investigated and discussed. Fluid dynamic numerical calculations were carried out to correlate and explain the experimental results. The cross-sectioning of the ceramic models after exposure (examined by SEM) showed a compact scale of zirconia (20 μm thick) underlying an external silica thin coating. A partially SiC-depleted region, a few microns thick, underneath the zirconia sub-scale was also seen. The post-test analyses confirmed the potential of the ZrB2–SiC composite to endure re-entry conditions with temperature approaching 2000 °C, thanks to the formation of a steady-state external multiphase oxide scale. Numerical calculations, which simulated the chemical non-equilibrium flow around the ceramic model, matched well the experimental results only assuming a very low catalytic surface behavior.